Friday Feedback: Pasta, the New Kale?

Study suggests carbs aren't the devil after all

A study this week suggested that Italians who ate a lot of pasta had lower BMI, waist circumference, and waist-to-hip ratio than those with lower intake. Yet numerous other studies have implicated carbohydrates as the chief contributor to the "obesity epidemic" of recent decades, at least in the United States. Also, as with so many diet studies, this one relied on participants' recall of their dietary habits.

We contacted nutrition experts via email to ask:

What do you make of this study?

How reliable and clinically significant can a single-food study like this ever be?

Do we yet have a good handle on what aspects of diet are most important for driving weight gain and obesity?

Movsas: The article reports on two studies conducted in Italy. The findings suggest that pasta, when part of a healthful Mediterranean diet, can be weight beneficial. The study seems to be in response to the recent decrease in pasta consumption as a result of the popular low-carb diet craze. Of note, one of the studies was partially funded by the Barilla [pasta] company. The results were not surprising. They echo the U.S. evidence based dietary guidelines that emphasize a healthful eating pattern -- the sum total of foods eaten over time -- taking into account all foods. Unfortunately, as has been seen in the past, findings like these often get misinterpreted and distorted by the press and private sector and can result in people believing that pasta is a magic bullet for weight loss. There is no magic bullet.

Srinath: Very intriguing study because of the focus on pasta, a food we usually suggest to our patients to limit due to concern about excess carbohydrates causing weight gain. Results suggest that intake of pasta was associated with lower body mass index, and less presence of obesity. This affirms the benefits of the Mediterranean type diet-which focuses on whole grains, lean meats, fish, and olive oil. Important to keep in mind that Italian population may be different from U.S. population and their overall diet, calorie intake, portion sizes, activity levels may be different.

Diekman: This study has some limitations that make it hard to say that pasta prevents weight gain but what it does demonstrate is that no single food is the cause of weight gain or obesity.

Lichtenstein: The study is provocative but one should be hesitant about drawing conclusions from single food studies. An important point to note is the differences in characteristics among the under/normal weight, overweight and obese individuals in the two cohorts included in the analyses. Among individuals in the Moli-sani cohort higher BMI was associated with older age, lower socioeconomic status and less physical activity. Similarly, among individuals in the INHES higher BMI was associated with older age, a lower percent reporting non-manual professions and less physical activity. How these affected self-reported pasta or other components of the diet is unclear. However, the energy intakes relative to the body weight status for some of the categories are implausible, making it difficult to interpret the study results.

Katz: There has long been evidence of health and weight benefit from a traditional Mediterranean diet, clearly among the "best" diets. In this paper, habitual intake of pasta is a strong correlate of adherence to a traditional Mediterranean dietary pattern overall. So, any apparent benefits may relate to pasta intake per se, but are more likely a byproduct of the overall dietary pattern, for which pasta intake is serving as a banner.

Heller: This study suggests that those who follow a Mediterranean type of diet that includes pasta are more likely to maintain a healthy weight, have a lower body mass index and waist circumference and waist-to-hip ratio and a lower prevalence of overweight and obesity. In this study, the portions that saw the health benefits were approximately 50-60 grams or 1 cup cooked pasta and pasta intake was associated with other foods such as tomatoes, tomato sauce, onions, garlic and olive oil. In the U.S., pasta portions in restaurants can be up to four cups per servings, doused with creamy, cheesy, meaty sauces and loaded with sodium. This is not what is meant by a traditional Med diet. When you make pasta at home, you will find a little goes a long way by adding loads of vegetables such as broccoli, spinach, zucchini, carrots, or mushrooms.

Single-Food Studies

Katz: This study really can't isolate a single food. In fact, no dietary study can – although metabolic ward interventions can get pretty close. Inevitably, eating more of "x" as a percent of calories means eating less of "y"; any one food change reverberates through the diet. We have strong evidence in favor of whole grains and benefits related to both weight and health -- so a benefit from whole grain pasta is certainly quite plausible. But even more plausible is benefit from an overall dietary pattern, for which routine pasta intake serves as a marker.

Stern: There are limitations of a single food study but I believe that this will stimulate future work.

Heller: Assessing dietary patterns and their relationship to health and disease is more meaningful than singling out nutrients or foods. In this case the Mediterranean approach to eating appears to have positive effects on weight management. It is important to point out that the Mediterranean diet is a lifestyle not a diet per se, and varies depending on the culture in which it is followed. That said, who doesn't love pasta? But don't go running out to your favorite chain restaurant and order pasta thinking it will help you lose weight. Pasta portions matter and what is on the pasta matters.

Lichtenstein: It is challenging to interpret data from single-food studies because it is impossible to determine whether the putative factor is the food itself or the compensatory food. For example, if someone reports eating more pasta did they eat less cheese or meat, less fish, less bread or did not compensate with other foods and/or beverages. We cannot tell from the data as presented. However, we would expect, from a clinical perspective, the response would be different among these four theoretical options.

Srinath: Difficult to say [how reliable and clinically significant a single-food study can be] because a healthy diet should be balanced and not focused on a single food or food group. This study is reassuring in that pasta intake was not associated with weight gain.

Diekman: Single-food studies are interesting but as a registered dietitian what I tell my clients is that it is about the whole, what does the whole eating pattern look like, not just a single food. What is nice to see in this study is that the current fad of avoiding carbs and/or gluten doesn't seem to be needed to achieve a healthier weight.

Movsas: Diet studies are fraught with problems and it would be a mistake to use the results from this study as proof that pasta can benefit weight. These were epidemiological studies that showed a statistical association between pasta intake and lower weight in a specific population. They did not show that pasta was the cause of lower weight. Even with statistical manipulation, it may have been something other than the pasta that was responsible for the weight benefit. In addition, information on food intake is mostly obtained through self-report. In the two studies reported in this article, the findings are based on information provided by participants through phone interviews and questionnaires. It is well known that people, understandably, under-report food intake. In this paper, one of the studies even used self-reported weights.

Weight Control

Stern: We still don't have an idea of what aspects are most important for driving weight gain and obesity. This is well illustrated by the United States Dietary Guidelines. In the early 1980s, the recommendation was to eat more carbohydrate and less fat. In the 1990s, the recommendation was that we eat more fat and less carbohydrate. There was an unanticipated consequence the increase in type 2 diabetes. I think that there is consensus at the moment that "regular" exercise is important for the maintenance of weight loss.

Lichtenstein: Because we have yet to figure out a way to sidestep the first law of thermodynamics, the most important factor driving body weight is energy balance; the number of calorie we consume and the number of calories we burn. There are many ways to create an energy deficit, decreasing overall food and beverage intake, decreasing the intake of selected components of the diet, increasing physical activity or a little bit of each. We also know it is relatively easy for many people to make short-term dramatic changes to their diet that result in weight loss. However, in the majority of case that does not help in the long run -- for sustained weight loss and maintenance, changes need to be made that are sustainable. Rarely does that come with changing the intake of a single food or beverage.

Diekman: As an RD, my first reaction to this study was -- we need to quit "demonizing" single foods and focus on choices and portions -- back to the basics. Utilize MyPlate for the right food choices and learn proper portions.

Katz: The reality is that a wide variety of diets have been shown to promote vitality, longevity, and weight control – but all such diets adhere to the same basic theme. They are made up mostly unprocessed, or minimally processed vegetables, fruits, whole grains, beans, lentils, nuts, seeds, and water for thirst. They can include or exclude eggs, dairy, meat and fish; they can be high fat, or low. That theme works every time. But again, it is the overall dietary pattern that matters most – not any one food.

Heller: The weight gain and obesity we see in people in the U.S. who eat the typical Western diet is driven by savvy marketing, chemical manipulations of highly processed foods to induce cravings for those foods, sedentary lifestyles and a whole lot of other complex environmental, physiological, and societal influences. Making more fresh, meals at home, managing portions, consuming a more plant based diet and increasing physical activity can make a big difference in our health and weight.

Srinath: Excess intake of calories will continue to drive weight gain and obesity. We know that excess intake of sugar-sweetened beverages, simple sugars, processed foods leads to weight gain but more research is needed regarding which other aspects are most important.

Movsas: We used to believe that weight was simply about calories in and calories out and following a diet was the answer. We are now realizing that weight determination is much more complex and that our calorie intake and expenditure are not just about will power. Weight is influenced by so many factors, some of which may not be in our control. Genetics, sleep habits, hormonal signaling, and even our environment in utero are just some examples of what is being studied in relation to obesity. The good news is that there is strong evidence that a modest weight loss of 10-20 pounds is achievable, sustainable, and adequate to significantly benefit health. This can be achieved through realistic, step-by-step lifestyle changes as opposed to going on a diet or believing a single food is the answer.

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